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NATURE 



[February 15, 1906 



from the Cripple Creek volcanic centre are somewhat 

 modified ; the various rock types recognised by him are 

 shown to be linked by intermediate forms; they are clearly 

 all divergent eruptive facies of one general magma, 

 characterised by containing from 9 per cent, to 15 per cent, 

 of potash and soda, the soda being always somewhat higher 

 than the potash ; no true andesite is recognised. Most of 

 the ore has come from the central area of phonolitic 

 breccia. 



The bulk of the telluride ore-bodies is in fissure veins, 

 either simple or complex, being closely spaced and linked 

 together, constituting what is called a "sheeted zone." 

 The fissures radiate from a point to the north of the area ; 

 they are uniformly narrow, therefore the amount of gangue 

 and ore is comparatively small. Quartz, fluorspar, and 

 other minerals usually line the walls of the fissures ; the 

 rich tellurides are generally the last minerals to form. The 

 authors consider that the unoxidised ore deposits represent 

 the product of one period of general mineralisation not 

 appreciably modified by any secondary enrichment. The 

 last exhalation of the Cripple Creek volcano seems to be 

 a mixture of nitrogen with about 20 per cent, of carbon 

 dioxide and a small amount of oxygen. The gas increases 

 in quantity with the depth, and in some cases interferes 

 seriously with mining operations. 



An interesting description of the petrography of the 

 Highwood Mountains of Montana (7) is given by Prof. 

 Pirsson. This region is occupied by a greatly eroded group 

 of volcanoes which were in activity at some time sub- 

 sequenl to the Lower Cretaceous; several necks (stocks) are 

 exposed, and now stand up as prominent peaks. High- 

 wood Peak, the highest point in the group, is composed 

 of syenite (pulaskose) and monzonite (shoshonose) ; in 

 East Peak the rock is a basic leucite syenite. The Shonkin 

 stock is shown to consist of Missourite, passing by inter- 

 mediate stages into shonkinite. The Arnoux stock is 

 important as the source of a new variety, Fergitsite 

 (fergusose), a rather coarse-grained, pseudo-leucitic augite 

 rock, consisting of orthoclase, nepheline, and diopside ; it 

 appears to bear a similar relation to the leucitites that 

 missourite does to the leucite basalts. In describing the 

 petrographic characters of the necks, dykes, and extrusive 

 flows, the new nomenclature is used concurrently with the 

 old, so that the conservative reader need not be dismayed 

 by " Trachyphyro-Highwoodose," " grano-shoshonose," or 

 what not. The author concludes with some suggestive 

 remarks on magmatic differentiation. 



The annual report of the United States Geological 

 Survey (8) is, as usual, a record of excellent organisation 

 and of abundant energy in all departments. 



The twenty-ninth annual report on the geology and 

 natural resources of Indiana (9) contains a monograph of 

 some 650 pages, by Prof. Blatchley, on the clays and clay 

 industries of the State, the reports of the inspectors of 

 minis and natural gas, a paper on the utilisation of convict 

 labour in making road material, an account of the petro- 

 leum industry in Indiana in 1904, and a paper on the 

 insect galls of Indiana. 



The section on clays is very much like similar reports 

 with which we are becoming daily more familiar; it is an 

 excellent report of its kind. It describes in detail the clay 

 resources of each county, with geological information and 

 analyses ; suggestions are given as to available clavs and 

 shales that are as yet unworked, and advice is given as to 

 the best way of dealing with them. The use of bricks for 

 road-making is strongly advocated, and the full specifi- 

 cations for the construction of brick pavements in the city 

 of Terre Haute are given ; these may prove of interest to 

 those in this country who favour this tvpe of road — the 

 brick roads in Terre Haute have given great satisfaction. 

 The report is illustrated with photographs and maps, and 

 with full statistics of the various branches of the clay 

 industry. 



The paper on insect galls, by Dr. Cook, is little more 

 than a catalogue of the galls known in the State. It is 

 provided with a simple introduction to the subject and a 

 bibliography, and with numerous outline sketches and 

 photographs. It should be appreciated in the Slate. We 

 are not aware that the papers mentioned above are issued 

 separately; if this is not the case it seems unfortunate, for 

 they appeal to such divergent interests. 



NQ. 1894, VOL. 73] 



The summary report of the Geological Survey of 

 Canada (10) for 1904 indicates considerable activity in all 

 quarters of the Dominion. A striking illustration of the 

 usefulness of the survey lies in the discovery of a coal 

 seam 10 feet thick in a bore-hole 2340 feet deep in Cumber- 

 land, Nova Scotia. This bore-hole was sunk through a 

 thick cover of unproductive rocks at the suggestion of Mr. 

 Hugh Fletcher, of the Geological Survey staff, after he- 

 had worked out the structural geology of the district. 



In the Purcell Range, Dr. Daly records an enormous 

 sill of hornblende-gabbro, 2500 feet thick ; this he calls 

 the " Movie sill," from its occurrence at a point where 

 the Moyie River crosses the international boundary. This 

 great mass of basic rock has been thrust into the pre- 

 Cambrian Kitchener quartzite, with the result that its 

 upper portion, some 200 feet thick, has been converted 

 into an acid biotite-granite by assimilation of the siliceous 

 sediment. This has come about principally through the 

 agency of " gravitational differentiation " following the 

 shattering of the quartzite by the heated contact. 



Prospecting for iron by means of the magnetometer 

 (Thalen-Tiberg form), an innovation in Canada, seems to 

 have had good results in Charlotte County, New Bruns- 

 wick. Dr. Barlow contributes some notes on the occur- 

 rence of corundum in the intrusive complex of Robillard 

 Mountain at Craigmont. The corundiferous rocks are of 

 syenitic or gabbroid type ; scapolite and nepheline often 

 accompany or replace the prevailing felspars. Some of the 

 svenite contains as much as 34 per cent, of corundum. 



J. A. H. 



THE PERIODICITIES OF SUN-SPOTS.' 

 "EVERYBODY knows how to interpret the curve by 

 means of which the intensity of radiation of a body 

 is expressed in terms of the wave-length or frequency, 

 and everybody recognises the utility of such a curve. It 

 allows us at once to distinguish between the line spectrum 

 and the spectrum of bands or the continuous spectrum, 

 and brings out regularities which would be difficult to 

 recognise in the original disturbance. In practice we 

 employ the spectroscope to give us the data from which 

 the curve of intensities is constructed. But what the 

 spectroscope can do for a luminous disturbance, calculation 

 can do for any quantity which fluctuates about a mean 

 value. We are able, therefore, to construct in every case 

 a curve which in all respects is analogous to the graph 

 which connects the period and intensity of radiation. This 

 curve I call the periodograph, and refer to the diagram 

 embodying the curve as the periodogram. There is a 

 periodogram of rainfall or barometric change, and these 

 curves would, in my opinion, if constructed for different 

 localities, yield us most important and characteristic in- 

 formation about climate. 



During the last three years I have been occupied in- 

 calculating the periodogram of sun-spot variability. The 

 results have been communicated to the Royal Society, and' 

 the following is a summary of abstracts which are pub- 

 lished in the Proceedings of that society. The first paper 

 deals with a detailed examination proving that the process. 

 I employ furnishes an analysis which is identical with the 

 experimental spectrum analysis supplied by the grating. 

 In the second paper the method is applied to the statistics 

 of sun-spots. 



The data used were Wolf and Wolfer's sun-spot 

 numbers, which give us sufficient information from the 

 year 1740 to the present time. I have in addition used,, 

 wherever possible, the measurements of areas which for 

 each synodic revolution of the sun have been collected 

 by the Solar Physics Committee of the British Board of 

 Education from the year 1832 onwards, and the areas 

 measured from photographs at the Greenwich Observatory- 

 for each day of the year since January 1, 1883. 



The whole of the observations were treated collectively, 

 but the complete interval of 150 years was also divided, 

 into two nearly equal portions, which were separately 

 examined. At first sight, the results obtained by a com-. 



1 Abstract of two papers, entitled, (i) " The Periodogram and its Opticar 

 Applications " ; (2) "The Periodicity of Sun-spots." Read before the Royal 

 Society on December 7, 1905. 



